Method of generating highfrequency oscillations



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METHOD OF GENERATINGHIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4,1940 10 Sheets-Sheet '2 j IN VE/V TOP.

DAV/D H. 5!. 0.4M.

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July 23, 1946. D. H. SLOAN 2,404,541

METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4,1940 10 Sheets-Sheet 3 INVENTOR'.

DAV/D H. SLOAN.

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D. H. SLOAN 24%,541

METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Jufiy 23, ma

Original Filed Nov. 4, 1.940 10 Sheets-Sheet 4 INVENTOR. DAV/D H. SLOAN.

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METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4,1940 10 Sheets-Shet 5 INVENTOR.

' DAV/0 H. SLOAN. I

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July 23, 1946. D. H. SLOAN 2,404,541

METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4,1940 10 Shee ts -Sh eet'6 2 47 ear,

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July 3, 1946. D. H. SLOAN 9 METHOD OF GENERATING HIGH FREQUENCYOSCiLLATIONS Original Filed Nov. 4, 1940 10 She ets-Sheet 9 a .395 as:

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D. H. SLOAN July 23, 194%.

METHOD OF GENERATING HIGH FREQUENCY OSCILLATIO NS Original Filed Nov. 4,1940 Patented July 23, 1946 METHOD OF GENERATING HIGH- FREQUENCYOSCILLATIONS David H. Sloan, Berkeley, Calif., assignor to ResearchCorporation, New York, N. Y., a corporation of New York Originalapplication November 4, 1940, Serial No. 364,284. Divided and thisapplication June 9, 1941, Serial No. 397,233

Claims.

This invention relates to electronic tubes, and particularly to tubesadapted for the production and modulation of ultra-high frequencyoscillations, i. e., oscillations of frequencies of the order of 1,000megacycles. This application is a division of my prior applicationSerial No. 364,284, filed November 4, 1940.

The progress of electronic and radio development since the inception ofthe art has been marked by two steady advances. One of these advanceshas been toward higher power, the other toward higher frequencies. Thelatter line of advancement has been, to a certain extent at least,incompatible with the first, since with increasing frequency the effectof interelectrode capacity has become greater and more troublesome.Neverthless, up to the last few years, the diihculties have been met bya steady evolutionary process consisting in large degree of refinementin detail, which has enabled the vacuum tube art to keep pace with theincreasingly rigid demands of the manufacturers and operators oftransmitting and receiving apparatus.

The attempt within recent years to carry the useful spectrum into therange of wavelengths in the range of a meter and less has involveddifiiculties of a new order of magnitude. For one thing, the frequenciesinvolved are so high that the transit time of an electron stream acrossthe interelectrode spaces of the tubes becomes an appreciable fractionof a cycle. For another, even with connecting leads reduced to minimumlengths, their inductance has been suflicient so that the capacitiesrequired in tuning them to the desired frequencies are small incomparison with the interelectrode capacities in conventional tumstructures and these capacities have therefore become not merely anuisance, limiting the efficiency of operation, but frequently anabsolute bar to such operation; so much so, in fact, that it has beenonly with tubes of very small size and consequent small power outputthat operation has been obtainable at all.

There therefore exists at the present time a need for a tube which willmeet the severe requirements of producing large power outputs byeneration or amplification at extremely high frequencies. Theserequirements are first, a cathode-grid structure which will effectivelymodulate an electron stream without the application of excessive controlvoltages; second, a cathode-grid structure whose capacity and inductancerelationships are so proportioned that they may be tuned to the highoperating frequencies desired; third, a structur lending itself tocircuits of low relative radio-frequency resistance of highlimpedance,so that excessive energy will not be required to swing them through thenecessary range of control voltages; fourth, fixed relationship betweenthe various elements, irrespective of temperature or ordinary shock, sothat the frequency to which the device as a whole is tuned will not beaffected by relative changes of position; fifth,

radiation minimum undesired or incidental from the various elements ofthe tube and its auxiliaries; sixth, a minimum of insulating materialsubjected to high-frequency fields. To these may be added the secondaryrequirements of demount ability for replacement of filaments; facilityin water cooling and avoidance of hot spots, and case 7 of tuning.

From the conventional approach these degree of control requires closespacing of cathode and grid, which leads to high inter-electrodecapacity. Rigid structure ordinarily means mas sive structure, whichagain leads to high interelectrode capacity. Water cooling systems tendto form effective antennae, leading to large "stray power radiation. Thebroad'purpose of my invention is therefore to reconcile these and otherapparent incompatibles.

Pursuant to this general purpose, among the objects of this inventionare: To provide a' tube which is capable of producing many kilowatts of'power at extremely high frequencies; to produce a high frequencygenerator of great frequency stability; to produce a high frequencyamplifier and oscillator tube of relatively high efiiciency,- andparticularly to produce such a tube wherein the losses due to undesiredradiation from the tube itself are reduced to negligible proportions;

to produce a high frequency oscillator and amplifier which may be tunedto operate at any desired frequency throughout a reasonably wide" range;to provide a high frequency oscillator and amplifier which may beconstructed with thehigh' degree of accuracy required to meet the closetolerances demanded by the frequency of operation and to maintain thosetolerances under the changes of temperature produced by suchoperafrequencies, in order to produce extremely short require- 7 mentsare incompatible to a large degree. A high and effective method oftuning apparatus ofthe character described; and to provide a type ofelectrode support for high frequency electronic devices which is massiveand rugged; andwhich, at the same time, does not introduceinterelectrode capacities which either severely limit. the frequenciesupon which the deviceis operative or the power which may be developed atsuch frequencies.

My invention possesses numerous other'obje'cts and features ofadvantage, some of which, togetherwith theforegoing, will be set forthin the following description of. specific apparatus em.- bodying andutilizing my novel. method. It is therefore to be understood thatmymethod is applicable to other apparatus, and that 1. do not limitmyself, in any way, to the apparatus of the present application, as Imay adopt various other apparatus embodiments, utilizing the method,within the scope of the appended claims.

The tube of my invention involves two basic concepts. The first ofthese. comprises forming electrode supports of sturdy coaxial metalliccylinders which constitute a radio-frequency transmission line of atleast one and preferably a plurality of quarter wave-length electricallinks, with impedance irregularities at or near certain of the quarterwave points, the electrodes themselves forming a portion of thesetransmission lines as considered electrically. Means are preferablyprovided for varying the position of the impedance irregularities toprovide exact tuning; but this is not essential since, as will hereafterbe shown, by a proper combination of the characteristic impedances ofthe quarter-wave sections and their terminating impedances, itispossible to make the: radio-frequency impedance of the supports asviewed from the electrodes themselves extremely high, so that theoverall effect isalmost: as though the electrode capacities togetherwith the: inductances required to resonate them were supported freely inthespacewithin' an unbroken metallic shield This latter feature issecured by providing multiple coaxial line sections forming'branchpathsof greatly different impedance, certain of these paths actin asIcy-passes f negligible impedance at points where it is necessary thatsome' circulating currents should flow, although D.-C. insulation mustbe maintained, whileat the same time maintainin the high impedancedesired in other paths which would otherwise lead to radiation. Byplacing these bypass sections at current nodes, the FR lossestherein'may be made too small toneed consideration.

The second fundamental concept comprises mounting on the ends of suchsupports, preferably in biaxially symmetrical configuration, one or a;plurality of cathode=grid combinations which act, as before stated, asthetermini of the transmission lines formed by the supports; mountingthe grid opposed to an anode or other accelerating' electrode in suchmanner as to produce an electrostatic field between grid and acceleratorwhich comprises lines of force very sharply curved in the immediateneighborhood of the grid; and

mounting the cathode in the region of sharpest curvature. One of thebest ways of obtaining such a structure is to form the grid of pairs ofcylindrical urfaces whose axes are parallel to the plane of the anode,and to make the cathode as. a filament or strip having a flat orslightly concave face lying between the cylindrical surfaces of thegrid. This results in the lines of force from accelerator or anodenormally terminating in the grid structure, none of them reaching' thecathode, from which emission is therefore normally suppressed. A fewvolts relative change. in. potential. of the cathode, as referred toeither accelerator or control grid, results in some of the lines offorce from the accelerator terminating in the cathode surface, which isaccordingly subjected to an extremely powerful field causing very largeemission to the anode. The result is what may be termed an explosivetype of emission, giving electron bursts of high density for very short.periods. at the peaks of the cycles. It will be evident that thisstructure results ina relatively high capacity as between cathode andgrid, but the tuned transmission:

line support enables this capacity to be effectively resonated with aninductance as smallas may be desired and still form a sharply tuned,high Q circuit whose high resonant input impedance may appear asresistive, capacitive or inductive as the conditions of operation mayrequire.

Referring to the drawings:

Fig. 1 is a longitudinalsection through a highfrequency oscillator tube.embodying my invention, the particular tube. illustrated employing aradial arrangement of. filaments and grids.

Fig. 2 is a transverse section of the tube of Fig. 1, showingthe-multiple coaxialgrid-filament sup ports, and water connections forcooling the filament mounting, the plane of section being on the line2-2 of Fig. 1.

Fig. 3 is a transverse sectionthroughthe anode structure of the tube,the plane of section being indicated by the line 3-3 of Fig. 1.

Fig. 4 is an enlarged detailed view illustrating water-coolingconnections from the exterior of thetube to the filament mounting.

Fig. 5 is a schematic sectional view through filaments, control grid,accelerating grid, boundary grid, and anode of the tube.

Fig. 6 is a sectional view through the. grid support line, showing theradio-frequency bypass between accelerating and boundary grids and thetuning mechanismfor isolating. the con.- trol grid and water cooling,the same.

Fig. '7 is. anenlarged detail showing the method of insulating certainofthe. supporting. rings upon which the coaxial electrodeelements arecarried.

Fig. 8 is a section taken atright angles. to the viewof Fig. l,andshowing theanode-supporting, cooling, and tuning system.

Fig. 9- is a perspective View of the accelerator grid.

Fig. 10 is an elevation of the control-grid-structure.

Fig. 11 is a sectional view, taken on the plane between the filament andgrid structures, and showing in detail the filament support.

Fig. 12 is a fragmentary axial. section taken on the line l2l2' of Fig.1.1.

Fig. 13 is an elevation. of the active face of the anode.

Fig. 14 is a fragmentary section of'theanode, the plane of section beingindicated by theline |a' r4 in the preceding figure.

Fig. 15 is an. elevation of the boundary grid;

Fig. 16 is a sectional view taken on the line Iii-l6 of Fig. 15, andshowing a portion of the anode in elevation.

Fig. 17 is an elevation of one of the filaments.

Fig. 18 shows a modified form of coaxial line structure forgrid-filament support in a tube generally similar to Fig. 1, but adaptedfor use either as an amplifier or an oscillator with inductivefeed-back.

Figs. 19, 20 and 21 are sectional views through the tube of Fig. 18,taken on the lines numbered in accordance with the figures.

Fig. 22 is a longitudinal section through a tube built in accordancewith this invention but wherein a cylindrical, rather than a radialfilamentgrid and anode arrangement is used.

Figs. 23, 24 and 25 are transverse sections through the tube of Fig. 22,taken on the lines indicated by the respective numerals.

Figs. 26 and 2'7 are detailed views indicating the tuning mechanism forthe tube of Fig. 22.

Fig. 28 is a longitudinal section on a larger scale through the filamentsupport of the tube of Fig. 22.

Fig. 29 is a transverse section through the supporting columns of thetube of Fig. 22, showing the construction of the centering mechanism,the plane of section being indicated by the line 29-29 of Fig. 28.

Fig. 30 is a sectional view taken on the line 30-30 of Fig. 22.

Fig. 31 is a fragmentary section taken on the line 3l3l of the precedingfigure, showing the passage of the cooling pipe past the anode andbetween the two sections of the filament support.

Fig. 32 is an impedance diagram for an openended, half-wave lengthsection of transmission line.

In the ensuing specification the invention will first be described inits various aspects as applied to an oscillator tube of moderate power(i. e., approximately 10 kw. peak output at 20 to centimetersWavelength). Following this there will be described two modificationsillustrating respectively the application of the principles of myinvention to a similar tube adapted for amplification or for generationof oscillations by inductive feed-back, and to a somewhat higher outputdevice showing the principles as applied to a tube constructed withcylindrical rather than radial arrangement of electrodes.

The tube shown in longitudinal section in Fig. 1 is of the demountable,constantly umped type, as, in fact, are all of those herein describedalthough the principles involved are not limited for use in such tubes.From the structural point of view the tube comprises a series of flangesconnected by sections of tubing and held together in compression. From apractical point of view it is advantageous to have the flanges piercedfor and held by circumferential bolts to hold the parts firmly inposition when the tube is not under vacuum, but when in use the externalir pressure tends to hold the entire device together, and the tube hasactually been operated without the retaining bolts, these have thereforebeen omitted in the drawings since they add a further complexity ofdetail to an already complex structure.

Considering for the moment, therefore, only the external structure whichforms the housing and which supports the remainder of the equipment, thetube comprises an anode housing flange I which is grooved to receivetightly the end of a tubular anode housing 2.

This housing fits an internal recess or counterbore in an annular gridflange 3, clamping a boundary grid 4 between the housing tube 2 and theflange 3. A rabbet on the outer periphery of the flange 3 receives oneend of a main support cylinder 5, whose other end terminates in anotherannular flange I. All of the parts thus far mentioned are of metal, andI have found it convenient to make the flanges of steel, and the tube 5also of seamless steel tubing, while the cylinder 2 may be eitherchromium or copper plated steel or solid copper, with copper preferredsince it forms a portion of a resonating circuit. Carrying on from theflange l is a glass or Pyrex cylinder 2 which abuts a terminal flangeI0.

As has been mentioned already, the device as whole is fully demountable.The ends of the tubes contact the flanges with smooth machine fit's.The. joints thus formed are sealed by applying thereto ordinary wideelastic .bands as indicated by the reference characters I I these bandsbeing smeared before-application with a small amount of vacuum linestop-cock grease.

It may be pointed out at this time that all or the structure thus fardescribed with the exception of the terminal flange It is at D.-C.ground potential, and as will later be shown in detail that the'entireexterior structure is substantially at radio-frequency ground. Thismeans thatthe insulating section formed by the cylinder 9 'is notsubjected to R.-F. fields. It also renders easy the support of thedevice by any desired external means, Part of such support may be theconnec-'v tion to the pump, which is by a pipe l2 of relatively largeinterior diameter, welded or otherwise secured'into the bottom'of theanode hous-. ing 2. This pipe is not shown in Fig. 1, butis clearlyvisible at the bottom of Fig. 8.

The various elements which contribute to the electronic action of thetube ar mounted within the envelope thus formed on columnar supportseach of which has transmission line characteristics designed to meet itsparticular function. These elements are shown in schematic arrange-'ment in Fig. 5, and comprise an anode 13, a boundary grid 4, anaccelerating grid 5, a control grid l6,'and a filamentary cathode l1. sFig. 5 is drawn to a greatly enlarged scale and shows a fragmentarysection of the'elements 00- operating with a single filamentary cathode.In

the tube here shown'six such cathodes are used and the portions shown ofthe other elements are repeated for each cathode. One advantage of thetype of structure here shown is that the ability of the tube to supplypower output varies almost' cerned it'is 'sufiicient for the present toconsider one only.

Considering, therefore, the 'portio-n'of the ele-.' ments shown in Fig.5, the anode i3, preferably 1 made of high conductivity oxygen-freecopper, is:

operated at the maximum potential'of the system, say 10 to 50 thousandvolts positive. It is provided with a V-shapedgroove 20 with'its axisparallel to the axis of the filament. Next; proceeding toward thefilament, is the boundary grid 4, which is also preferably made ofoxygen-free copper. This is provided withan aperture surrounded by acollar 2| in accurate alinement with the groove 23 in the anode. Next inline is the accelerator grid It, with an aperture 22 which is somewhatnarrower than the opening in the boundary grid, and which is operated ata potential above the cathode of from 5 to 20 thousand volts. Allpotentials mentioned are illustrative and relative only, since theactual values used will depend upon the size, power output and operatingfrequency of the device. Furthermore, modifications in design arepossible whereby the functions of certain of the grids are combined,other electrodes are operated at ground potential, etc. Suchmodifications will be considered later; the purpose here is to show thapplication of the principles of my invention to the present tube.

The most important portion of the combination is the arrangement of thecathode-grid structure. The important features here are first, that thecontrol-grid elements comprise parallel cylindrical surfaces, curved asthey are present ed to the filament. In the present case they are rodsor wires, but they could be cylindrical surfaces formed as the edge of aslot in a fiat plate without affecting their performance. Between thesesurfaces, and slightly back of the plane of their centers of curvature,lies the filament, which has a flat or preferably a slightly hollowground face presented to the anode. It is convenient to operate thefilament at ground potential (disregarding for the moment the slightvoltage drop along the filament) and, for the powers here considered, tooperate the grid [6 at 200 to 500 volts negative.

It will be seen that at the orders of voltages given the major fieldsare from the accelerator grid 15 to the control grid. As is well known.the lines of force constituting such a field terminate at right anglesto the surfaces of the fielddefining electrodes. It follows that in theregion adjacent the cathode the lines of force emerge from the gridwires in the general direction of the cathode and then curve verysharply toward the anode in a direction nearly at right angles to theirdirection of emergence. There is also a fairly strong field between thecontrol grid and the cathode itself, which is superimposed locally uponthe field between the control grid and accelerator grid, and is directedtoward, instead of away from the cathode. As a result of the interactionof these two fields none of the lines of force from the accelerator-gridnormally terminate upon the surface of the cathode. Emission hastherefore no tendency to leave the latter, since the space adjacent itis nearly neutral, with such weak field as exists therein directedtoward the cathode.

As is the case with any grid-controlled tube operated through cut-off,when the grid swings positive some of the lines of force from theaccelerator-grid which formerly terminated on the control grid nowterminate on the cathode, and as the cycle progresses thecathode-control grid field weakens or even reverses, permitting emissiontoward the anode, and a space charge builds up in the region immediatelyin front of the cathode face which has the usual effect of limitingemission. The distinguishing feature here is that the region where thefield is weak enough to permit such space charge effect is very shallow,so that even with the low velocities imparted to them by such relativelyweak field the electrons can and do traverse it in a reasonably smallfraction of a cycle.

The biasing potential between cathode and grid is so adjusted thatemission can occur only for an instant at the cycle peaks, and cut-offmay occur even before the first electrons emitted have traversed thespace charge region. Furthermore, While in this region there is amaximum difference of velocity as between electrons, both by reason ofdiffering initial velocities of emission and, more important, by reasonof differing acceleration due both to phase of emission and fieldstrength at various parts of the cathode surface.

The important point is that because the region is so shallow all of theelectrons emitted do get through it before the cycle has advanced toofar, and, having traversed it, fall into the region of high potentialgradient where acceleration toward the anode is very great; space chargeeffeet is of no further moment, and they receive so large a portion oftheir final velocity that their differences of velocity in the initialregion are immaterial.

It should be realized that while space-charge effect prevents someemission and decrease the acceleration of electrons emitted, it will notdrive those which have been emitted back to the cathode nor preventtheir reaching the anode. It follows that the space-charge region may beconsidered as a reservoir for emitted electrons. With conventionalgrid-cathode structures it is relatively deep, so that, at thefrequencies and powers at which this tube is intended to operate,transit therethrough occupies a major portion of the cycle, and with thevarying velocities obtaining while in this region the electrons stragglethrough to reach the anode in such varying phases that the densitymodulation of the stream is almost if not entirely lost.

With the arrangement of my invention, however, the space-charge regionis so shallow that even the stragglers among the emitted electronstraverse it in less than a quarter cycle and instead of the densitymodulation of the electrons being lost they reach the anode in bursts ofsuch power and suddenness and with such close velocity grouping that Ihave termed cathode-grid combinations of this type explosive. The objectof the design is to make the electron reservoir constituted by thespace-charge region as shallow as possible, and in practice the idealcan be so far realized as to permit density modulation of electronstreams at frequencies in the range of 1,500 megacycles, where in thepast it has been necessary to use velocity modulation, involving largerand more complicated structures, to get reasonably effective results,even in smaller sizes and at much lower powers than those herecontemplated.

When the tube here shown is used as an OS- cillator in the manner now tobe described, the various potentials are so arranged and proportionedthat the transit time of the burst of electrons is substantiallyone-half cycle. The anode I3 is in a tuned circuit, as is also the gridIS. The condition of oscillation then is that the potential of the anodeand the grid swing in the same sense, so that the grid reaches its peakof positive potential at the same instant as does the anode.

One of the results of the conformation of the electrostatic fields is astrong focusing action upon the electron bursts, and these burstsaccordingly fall upon an extremely limited portion of the anode surface,substantially none reaching either of the intermediate grids. The anodearea upon which the electron bursts impinge is that included in theV-shaped slot 20. The reason for this arrangement is to spread the areaof impact and so increase the size and decrease the intensity of maximumlocal heating, while increasing the cross-sectional area of thermalconductivity by which cooling occurs, and also to insure that secondaryelectrons are not projected into regions of high field intensity whichwould accelerate them so that they, in turn, would cause serious heatingeffects.

It has already been stated that the transit time of the electron burstis one-half cycle of oscillation, and it follows that immediately afterthe electron burst has occurred the anode has started to swing negative.The electrons accordingly reach their maximum velocity at or about theplane of the accelerator grid-ideally, just as they pass the effectiveplane of the boundary grid 4. As the anode continues to swing negativethey encounter a decelerating field, either in an absolute sense or, ifstill being accelerated by the D.-C. field, from the anode, at least incompari- 'son to the acceleration of the D.-C. field alone. In passingthrough this decelerating field the electrons are delivering energy tothe anode circuit, and they are traveling at minimum relative velocitywhen they enter the slot 20. This slot acts in some degree as a Faradayspace, and the electrons sufier little change in velocity or energy asthey pass through it. Therefore their Work is done and their transittime effectively over as soon as they have entered it.

Since the acceleration of the entire burst of electrons takes place withsubstantial uniformity they retain their close grouping at the time ofimpact, and since the impact occurs when the electrons constituting theburst have suffered maximum deceleration there is a minimum of energywasted as heat and the oscillator consequently operates at relativelyhigh eficiency.

For operation in the manner described the desiderata are that thecontrol grid l6 and filament ll should be efiectively isolated from eachother both as regards D.-C. and radio-frequency potentials, and shouldhave an effective capacity sufficiently low so that it may be tuned tothe desired operating frequency, or, in other terms, it must be capableof being connected in circuit with an inductance sufiiciently small totune to that frequency. The accelerator grid I must be insulated fromthe other elements to maintain its D.C. voltage, but should beeffectively grounded as regards radio-frequency potentials. The boundarygrid 4 should also be grounded to radiofrequency and for convenience inoperation and safetys sake should preferably also be grounded as regardsD.-C. potential, as it is electrically continuous with the envelope. Theanode should be free as regards both A.-C. and D.-C. potentials.

The various mounting and auxiliary means next to be described aredesigned to meet the desiderata as fully as possible. In thisdescription terms such as above or below are used to indicate positionas shown in Fig. 1. They have no other significance, as the device maybe operated in any position.

Starting at the bottom of Fig. l, with the flange I9, a highconductivity column or pipe 25 extends a major portion of the length ofthe entire device to the plane of the flange 3 and the boundary grid l,This column is brazed or otherwise permanently secured into the flangein so as to be accurately concentric with the remainder of the tubestructure and, of course, to be vacuum tight.

At its upper end it is threaded to receive a gridsupport ring 21,whichis clamped between locking nuts 29 and 30, and an additionallocking screw 3| (Fig. 10) is also provided for further security. Thepairs of parallel grid wires I6 project from the ring 21 parallel to itsradii, six pairs of grid wires being provided in the presentdesign, thepairs being equidistantly spaced around the periphery of the ring.

Two sliders are mounted on the column 25. The upper slider 28comprises'a short section of tubing 32 surfaced to a sliding fit on thecolumn 25 and shouldered at each end to receive discs33 and 34 betweenwhich a short section of tubing 35 is clamped. The column 25 is providedin this region with a longitudinal slot for the passage of a-screw 31which engages a piece of tubing 39 sliding within the column. The tubing35 terminates in an annular block 40, and an adjusting rod 4| isthreaded into one side of the block and passes to the exterior of thetube through a gland box 42 and a Wilson seal 43. It is apparent thatthe position of the slider may be adjusted by sliding the rod 4|.

A word. as to the Wilson seal may here be in order, and in thisconnection attention is drawn to the showing at thelower right of Fig.8. The seal proper consists of a normally flat washer 45 of synthetic ornatural rubber, which is forced against a conical seat 41 by theinternally conical edges of a gland 49. When the washer is unstressedthe aperture therethrough is slightly too small for the rod 5|! which itis desired to seal. The seal is lubricated with a small quantity ofvacuum stop-cock grease. Such a seal is vacuum tight under conditionswhere other known types of packing would leak badly, since thedifierential pressure on the washer serves to make it hug the centralrod more tightly and it remains tight whether the rod be subjected torotary or sliding motion in either direction.

Returning to the general tube structure, the second and lower slider 5|is essentially similar in construction to that just described, exceptthat its actuating rod 52 is mounted externally of the column 25throughthe gland box 42 and Wilson seal 53.

The slider 5| makes a close sliding fit within a cylindrical conductor54 mounted in the flange I0 accurately concentric with the column 25 andmaintained in this concentric relation both by the slider 5| itself andby an'auxiliary diaphragm or spacer 55. The tubing 54 does not extendthe full length of the central column, but terminates a distance abovethe flange 1 which is somewhere in the neighborhood of one-eighth of awavelength at the mean frequency for which the tube is designed.

Accurately coaxial with the column 25 and its surrounding conductor 5|is a third conducting cylinder 51, mounted on the flange 1 and extendingbelow it for approximately one-eighth wavelength, so that the twoconductors 54 and 51 overlap by a distance approximately equal toonequarter wavelength of the average operating frequency of the device,wavelengths in this sense being used to mean the wavelength of thefrequency transmitted along the two tubes as a coaxial transmissionline. There is no metallic contact between the two conductors 54 and 51,and they are separated by vacuum so that dielectric loss-does not occurin the space between them. r

Column 51 is brazed or otherwise secured in the flange 1, is made ofhighly conducting material (preferably oxygen-free copper) and ispreferably provided with a cooling system comprising a water pipe (59coiled around and soldered to the external surface of the column. Theends of this pipe are brought out through the flange l at the right ofFig. 1.

The upper end of the column 51 carries an intermediate ring 6! whichsupports indirectly one end of each of the filaments IT. The other endsof these filaments are carried by a group (here six) of pipes 62 mountedin the annular inter-space between the column 51 and the outer shell 5.The lower ends of the pipes 62 are mounted in a ring 63 which is boltedto and insulated from the flange l as is shown in Figs. 2 and '7. Thering 63 is counterbored at three equidistant points to receiveinsulating beads 64 of porcelain, lava, or other refractory insulatingmaterial which beads space the rings slightly from the flange I. A capscrew 65 passes in turn through a clamping cap 61, a second bead 69, therings 63 and the bead 54 to clamp the ring firmly to the flange. Itshould be noted that the potentials which this arrangement mustwithstand are of low frequency and are only those across the filament,i. e., the insulation need only be of sufficient value to withstand afew volts (three at 60 cycles in the instant structure) and theinsulating material is not subject to dielectric heating fromradio-frequency fields.

The actual filament mounting can best be seen in Figs. 11 and 12. Eachof the tubes 62 carries an inwardly projecting L-shaped lug l0, and theinner ends of the lugs are provided with slots H for receiving thedownturned ends of the stapleshaped filaments ii, the ends being clampedinto place by set-screws '12. The inner ends of the filaments areclamped in an annular groove 13,

formed in an inner mounting ring 'i' i which is supported on column 51by the intermediate ring 6! before mentioned. The actual clamping of thefilament ends is accomplished by pairs of setscrews 75 hearing on smallblocks H.

The pipes 62 are surrounded by open-ended cylindrical conductors 79,which terminate at the level of the upper end of the lug and extend downover the pipe 62 for approximately one-quarter wavelength and aresupported by the ring 6!. Within the conductors 19 are inner tubularconductors 6B of substantially the same length, open at their upper endsand mounted by their lower ends on the pipes 62 by means of conductiveblocks 8|. The concentric tubes 19 and 8B are both open at the filamentend, being notched to clear the lugs is and also being provided withalined holes to permit tightening of the set-screws 72. It will thus beseen that the only connection between the inner column El with itssupporting rings El and M and the group of filament support tubes 82 isthe filaments themselves.

These are shown in Fig. 1'7, and as will be seen are relatively shortand rigid. They are preferably of pure tungsten and have a considerabledegree of strength. It will further be seen that the support affordedtheir outer ends by the tubes 52 and lugs it is light and of smallinertia and that the tubes 62 have relatively large resiliency. Thefilaments therefore are very unlikely to be ruptured by shock on thedevice as a whole, and there is ample flexibility to take up theirexpansion.

Each filament is preferably formed of round tungsten wire, one surfaceof which is ground fiat or slightly concave. The diameter here used is50 mils. The grinding is preferably performed in a jig which deforms thewire slightly in the longitudinal direction, so that the endsof thefilament are ground a few thousandths of an inch thinner than is thecentral portion. This grinding forms the flat emitting surface of thefilament, and if done with a relatively small wheel whose axis ismaintained parallel to the length of the filament, it gives the slighthollow grinding which has already been stated to be advantageous. Theeffect of thinning the two ends, adjacent the point where the filamentis clamped, is to give a greater current density at these points, with aconsequent greater liberation of heat which compensates for the heatconduction to the clamping means and results in substantially constanttemperature and substantially constant emission over the entireeffective length of the filament. Being of pure tungsten, the filamentretains a degree of resiliency even at its emitting temperature, andthis, together with its resilient support, prevents buckling or changeof plane of the emitting surface when in operation and keeps theelectrical constants of the device fixed under such minor variations inoperating temperature and expansion, and inequality in these factors asbetween the several filaments, as inevitably occur in practice.

Cooling for the support of the inner ends of the filaments isaccomplished by conduction through the support rings M and BI to thecolumn 5'! and thence through the cooling coil 60. Coolin for the outersupports is by circulatory system within the support pipes 62themselves. A small water pipe 99 enters the side of each of the supportpipes 62, and extends axially within it to a point adjacent the lug HQ,50 that water entering this pipe will be squirted against the inner endof the lug. From there it returns through the pipe 62 externally of thepipe to the bottom of pipe 62, where the end 90' of the next pipe isconnected to carry the water to the next filament support, circulationthereby occurring through each of the support pipes 62 in succession.

The supply for this circulatory system is through a fitting designatedby the general reference character 9!, comprising coaxial pipes 92 andas which connect respectively to the two ends of the system. The outerof these pipes is permanently secured to the support ring 63 (see Fig.4) The fitting 9! passes through the flange 1 and is insulated therefromby insulating bushings 94 of steatite or other refractory between whichis a compressed rubber washer 95 forming a vacuumtight seal. Aconnecting lug 91 for connectin one filament supply lead is mounted uponthe fitting SI, and the ring 63, and the circulatory system comprisingpipes 90 and 62 all constitute the conducting systemfor supplying thefilament current. The return circuit is through the column 57 and thefiange 1, to which a second connecting lug (not shown) is attached.

There are two other features comprised within the filament-gridstructure and their supporting systems. The first of these is a slidingplug 99 mounted in the end of the inner support column 25, andadjustable as to position by means of an operating rod H33, and anoffset extension rod lfll passing through a Wilson seal I02 in the glandbox 42. The second is a. cooling pipe H23 which extends substantiallythe full length of the inner column 25 and is soldered thereto adjacentits upper end for better heat transfer.

We are now in a position to consider the electrical characteristics ofthe filament-grid structure in view of the desiderata above set forth,and it is believed appropriate to do this at this point, since the sameprinciples are involved in the supports for the remaining elements ofthe device and the explanation of all will be simplified if theseprinciples are in mind. The necessary separation of the elements asregards D.-C. or low frequency potentials have already been accountedfor. There is no metallic connection between the grid-support column 25and the filament-support system comprising the column 51, and thesupport pipes 62. Remaining to be accounted for is the impedancerelationship between the grid and filament members, and this isdependent upon the impedance of the coaxial transmission line formed bythe inner and outer columns 25 and 51 and the coaxial conductorsassociated therewith.

The impedance characteristics of transmission lines whose lengths are ofthe same order of magnitude as the wavelengths of electricaloscillations transmitted thereby are now well known, but they arerestated here for convenience in the explanations that follow. Most ofthem can be derived from the impedance diagram of a half-wave line openat the output end, as shown in Fig.32, which indicates such a linediagrammatically, and shows the approximate curve of relative impedancelooking into any portion of the line from the right, resistance of theconductors themselves being assumed to approach zero. Extremely shortsections show a high capacitive reactance, which falls to thecharacteristic impedance of of the line at the wavelength point, and tozero at the quarter-wave point, i. e., a quarterwave open-ended lineacts as a dead short. From this point on the apparent reactance isinductive, rising again to the value at the A point and approachinginfinity at A.

The same diagram may be taken as representing the impedance of ashorted-end line if the origin be taken at the nodal or quarter-wavepoint, which appears as a short when looking into the line. For shortsections the reactance is small and inductive, it rises to at the A; xpoint and approaches infinity at Since this appears as an open circuit,increasing the length of the line repeats the portion of the diagramshown at the left of the nodal point.

Stated in another manner, a quarter-wave open line or a half-waveshorted line appears much like a series resonant circuit, while aquarterwave shorted line or a half-way open line appears like ananti-resonant or parallel resonant circuit.

The only other relationship necessary to the understanding of thepresent invention is that the characteristic impedance of a quarter-waveline is the geometric mean between its input and closing impedances. Theshort-circuit and opencircuit conditions are, of course, merely specialcases of this general relation.

The lines comprising the element supports of the tube of my inventionmay be considered from 14 a number of aspectsall depending on thegeneral relationships above set forth, "but in the treatment hereadopted they are generally considered as divided into sections ofquarter-wave length, or thereabout, as'thisis believed to lead to thesimplest explanations. I

Weare interested in the impedance of the gridfilament support line asviewed from the grid end, but this impedance is dependent upon theterminating or output impedances of the various sections and, therefore,in order to determine what the grid-end impedance will be, we mustconsider the various elements, section by section, starting from theoutermost or lower end of the tube as shown in Fig. 1. c 7 7 From thisaspect the first section of the structure is the section including theadjusting rods 52, 4| etc., the flange I0, and the section of thetubular conductor 54 illustrated as below the end of the column 57.Electrically this portion of the structure is asingle conductor, andviewed from its upper end constitutes an end-fed antenna. It ispreferable that its length be of the order of one-half wavelength at theoperating frequency of the device, in which case its effective impedanceZ2 will be in the neighborhood of 1,000 ohms. If its length be reducedto one-quarter-wavelength its effective input impedance will likewise bereduced to the neighborhood of from 50 to ohms, the quarter wavelengthconditionbeing the least desirable in practice. This antenna isconsidered as being fed'by the coaxial transmission line comprising thetubular conductor 54 as the inner element and the column 51 as the outerelement. With the spacing shown such a transmission line will haveacharacteristic or surge impedance Zn of about 10 ohms, and as hasalready been stated the length of this section of transmission line isapproximately where A is the wavelength at the frequency of operation.If we consider the quarter-wave condition to be fulfilled exactly'theimpedance looking into the coaxial line from the grid end will be If.the antenna section of the system have an impedance of the order of1,000 ohms, the characteristic impedance of the line being 10 ohms, the

input impedance of the lin will therefore be 1 of an ohm. This lowimpedance therefore becomes the closing impedance of the section of lineimmediately preceding it. From one .point of vi'ewit acts as aradio-frequency by-pass between the inner conductor 54 and the outerconductor 51, so that viewed from the input end, at radio-frequenciesthe cylinder 54 and outer column 51 appear as a single conductor, andform, in connection with inner column 25, a single radio-frequencytransmission line considered as fed from the grid-filament end through aslight impedance irregularity where the inner cylinder 54 terminates.Its effect from another point of view will be considered later.

Even if the conditions as to impedance of antenna and length of thecoaxial line constituting the column 51 and cylinder 54 are not exactlyeighth wavelength, the input impedance will still be low in comparisonwith the characteristic impedance of the line, and although more powerwill escape than if optimum conditions are met the amount of powerwasted by such undesired radiation will be very small.

The section of the inner line comprising the cylinder 54 and column 25terminates in the slider 51, which, as it is of large area and makesgood contact with both conductors, ma be considered as of zeroimpedance. This section may be tuned to exactly one-quarter wave bymoving the slider. Due to the spacing between the two conductors thecharacteristic impedance of this section of transmission line is high,and if the resistance of the line were zero the input impedance would beinfinite. Actually it may always be made to exceed 100,000 ohms andunder optimum conditions may reach ten times this value. This sectiontherefore forms a tuned radio-frequency choke of extremely highimpedance interposed betWeen the filament-grid structure and the outsideworld, and the impedance involved is so high that practically all energyreaching it is reflected back to its source.

What actually happens can be expressed more nearly in the terms of lowfrequency power line transmission if we think of the antenna as a loadwhich is fed by a line terminating immediately above the top of thecolumn 511, Current fed to this line from the central column 25 mustproceed down the column, across the slider, and back to the top of theconductor 54, since owing to skin effect none will now transverselythrough the wall of the conductor, In so flowing the current meets anenormou impedancesay 100,000 ohms. From there the line continues downthe outside of conductor 54 to the antenna and back within the column-51 to the terminus above the top of conductor 54. This latter length ofline, including the load imposed by the antenna, has an impedance of,say, 1 ohm, and since the voltage available at the termini of the linewill divide itself across this low impedance and the high impedance linesection in series therewith in the proportions of the magnitudes ofthose impedances, and since the current flowing at the input points ofthe respective sections is the same, it follows that the energydelivered to the respective impedances will also be in proportion totheir magnitudes, and only 100.000 of that delivered to the line will betransmitted to the antenna to be radiated thereby-still less if optimumconditions are met.

From still a slightly different aspect, the small and largely resistiveimpedance offered by the outer line is at a current node. We thereforehave a very small current flowing, and therefore the value of PR isvanishingly small, the R in this case being the apparent input impedanceof the outer line and 1 B (practically) the ener y radiated.

From whatever aspect the matter be considered the result is the same:The sections of the transmission line above the current node terminatein what is equivalent to an open circuit, just as would a low frequencyline connected across an ordinarily good insulator. There is someconsumption of power, which can be neglected in further consideration,(as in the case of the insulator) and the succeeding sections can betreated as if they terminated at this point in an infinite impedance. Itshould be noted, however, that at the frequencies we are consideringsubstitution of an insulator for the line sections would drop the 16impedance to a finite value and introduce large losses through radiationand dielectric phenomena.

The design problem to be met, therefore, is the design of a structurewhich, when terminated by an impedance approaching infinity, will havethe properties of an anti-resonant circuit as viewed from cathode andgrid. This structure is provided by two additional quarter-wave sectionsof the same line,

The first of these sections extends to include the upper slider 28, andits design is such that its electrical length may be changed in oppositesense to its physical length; i. e., such that it may be fitted inbeneath the section above it even when the length of the upper sectionincreases with decreased frequency of operation or vice Versa.

This effect is obtained by means of the irregularity introduced by thelow-impedance line section constituted by the slider 28. From the top ofthe high impedance section already described to the slider is a lengthof relatively high impedance line of less than wavelength whichtherefore appears as a capacity variable from zero to some small valueas the slider is moved to change its length from zero toward To this isconnected the relativel great capacity of the slider portion of the lineabout A in length, but presenting an eifective capacity many times asgreat as and apparentl in parallel with that of the lower section, sothat moving the slider to change the length of the section below itchanges the apparent capacity as viewed from above relatively little.Therefore a very short length of the high impedance line above theslider is all that is necessary to tune this efiective capacity toresonance, thus completing the quarter-wave section of line and bringingthe node or quarter-wave point of the composite sec tion a smalldistance above the upper slider face. The distance between the sliderand the node will vary with frequency, of course, but only slightly withthe position of the slider.

It has already been pointed out that the node is effectively equivalentto a short-circuit, and hence, since by moving the slider we may movethe position of the node, by so doing we may tune the uppermost sectionof the line including the filament and grid. We have made that portionof the line below the slider and above the impedance loop relativelyineffective in tuning, so that we have an "elastic or extensiblequarterwave section of line.

The final or grid-filament section ma thus be resonated or otherwisetuned to give optimum operating conditions. In the case of Fig. 1, wherecapacity feed-back between anode l3 and grid cap 99 is used, the desiredtuning of this section must provide a capacitive reactance. This isobtained by making the grid-filament section slightly longer thanone-half wavelength or, in

other terms, tuning it to a slightly lower frequency than that of thedesired oscillation, so that as viewed at grid and filament it presentsa small anti-resonant capacitive reactance. Under these circumstancesthe filament-gridsystem appears as a capacity in series with thecapacity between the grid structure and the anode, and this lattercapacity is adjustable b varying the position of the cap 99. When,therefore, the potential of the anode swings, the grid will assume apotential with respect to the filament (and ground) which isintermediate between cathode and anode potential, and which bears theproportion to the total potential between anode and filament that theeffective series capacity between anode-grid and grid-filament bears tothe apparent capacity between filament and grid. In other words, thearrangement is essentially a capacitive voltage divider which swings thegrid potential in the same sense that the anode potential swings, and infixed and predetermined proportion thereto. Since the criterion foroscillation of the device is that the grid and anode should swing in thesame sense and in step, the result is a highly effective capacityfeed-back which is under control either by varying the actual capacitycoupling with the cap 952 or by varying the effective resonant inputcapacit of the grid-filament circuit by varying the position of theslider 28.

By the use of the two sliders the device is thus given its veryconsiderable tuning range. The lower slider El brings the current nodeto the point wher the antenna is fed; the upper slider 28 moves thenodal point immediately above it and thus tunes the filament-gridsection. The actual point of importance is that by adjusting theposition of the sliders the effective resonant impedance of thefilament-grid combination may be made to assume an value which may bedesired, since the node above the slider 28 may be moved near enough tothe rather large lumped cathode-grid capacity to embrace between thenode and that capacity the exact small line inductance required fortuning it. In actual practice the effective impedance will be madecapacitive and small in comparison with the physical grid-cathodecapacity, but it might, if desired, equally well be made inductive orresistive. Furthermore, since the effective resistances in the circuitare extremely low, the losses are also small even though the circulatingcurrents may be large.

A system of transmission lines, chokes and bypasses similar to that usedin the filament-grid circuit is employed across the filament to preventtransmission of energy to D.-C. insulation and to prevent filamentdamage by R.-F. currents. The actual ground point on the filamentcircuit is the flange l on the outer casing of the device. This,however, is unimportant and the efiect of the transmission linearrangement may be considered as though the ground point were at theinner end of the filament. This may be considered as terminus of aquarter wavelength coaxial transmission line comprising the tubularconductors 19 and 80, which is open at its lower end, terminating in ahigh impedance. The transmission line impedance is again low, being ofthe order of, say, 5 ohms, and the line therefore forms a negligibleseries impedance as before, acting as a Icy-pass to the inner conductor.This, again, is a quarter wavelength line with the pipe 62 as its innerconductor, terminating in a dead short, and therefore ofiering very highimpedance. As the potential imposed across this impedance is merely thatwhich can build up across the short filament, amounting to a few voltsat most, the escape of power through the filament support may beneglected, and the high impedance effectively in series with thefilament prevents circulation of R.-F. currents which might otherwisecause hot spots and burn-outs.

We are now ready to consider the mounting of the remaining elements, i,e., the accelerator grid,

shown in'elevation in. Figs. 9, 15 and 13 respectively; The acceleratorgrid is mounted from a side tube I05, which. is welded to projectthrough the wall of the housing 5 immediately below the flange 3. Thisside tube carries at its outer end a flange I01 which is surfaced toreceive the tubular glass insulator we, and the latter, in turn, carriesa terminal flange H0. This structure may best be seen in theflenlargeddetail view of Fig. 6. As in the case of the main tube envelope, thetie-bolts which'hold the structure together are omitted, but it will beunderstood that it is assembled in the same fashion as is th mainenvelope with ground surfaces reenforced by greased rubber bands orgaskets I II which'form' Two tubular conductors are fixed to.

the seals. and project inwardly from flange H 0. The inner conductor II2 is spaced from the outer conductor H3 and is held accuratelyconcentric therewith by an annular spacer H4. The accelerator grid I5 issupported from theinner member by a tubular bracket H5, the end of whichfits within the conductor H2 and is rigidly secured thereto. 'A coolingpipe I", bent into a ring to surround the accelerator grid, has its endsbrought down parallel to the support bracket H5 and enters the innerconductor on either side thereof, the ends of the pipe passing into theinter-conductor space distally of the spacer H4 and emerging through theflange H0. A tuning slider H9, which nearly fills the space between theinner and outer conductors and does not make actual contacttherebetween, is operated by means of a hook I20 whose end projectsthrough a longitudinal slot in the conductor H2. A controlrod I2 I isthreaded to the end of the hook and emerges through a Wilson seal I22.

The supporting bracket H5 and cooling tubes I H. are carried up to theinterspace between the control grid and the boundary grid through anangular fitting or shield I25, which passesthrough a notch I 21 cut inone side of the filamentsupport ring 6i. This construction is shown inFigs. 1,6 and 11, each of these figures showing sections of the shield.The shield is electrically continuous with a pan I29 overlying andcontacting th filament support ring; 14 and slotted immediately abovethe filaments, which forms an additional shield or barrier to separatecompletely the anode and control-grid sections of the tube except at thepoints where intercommunication is necessary or desired. The shield andpan therefore form one terminus, and the accelerator grid and coolingpipe] I'I form the other terminus of the radio-frequency transmissionline comprising the side tube I05 and the tubularconductors H2 and H3.

From what has gone before it is believed that the operation of thisarrangement will be readily apparent. Again we have an antenna systemcomprising the control rods I2I and cooling tubes I ll, plus theprojecting end of the conductor I I3, which is fed by and oifers arelatively high impedanceto a quarter wavelength transmission line oflow impedance formed by the side tube I05 and the conductor H3, andthere'is accordingly a radio-frequency by-pass between the groundedouter case 5 and tube I05 of the conductor H3. Within this there isanother series section of transmission line comprising the conductors H2and H3 and terminating in a short formed by the spacer-H4. This v-innerline is tuned to a quarter wavelength by means of the slider I20, whichacts as a loading capacity and 19 increases greatly the electricallength of the line. In practice this slider is moved back to a pointfrom which the line appears as a very large inductance at the operatingwavelength. The proper point is that at which the remaining inductanceand capacitance of the line, considered from the grid end, make it justa quarter wavelength from the inner end to the shorting spacer I I4,forming a very high impedance at the shield where the grid I and coolingtube II! are supported, and preventing any appreciable power beingtransmitted past this point to b radiated. The capacity of the grid I5to the boundary grid 4 is large, and that to the control grid I6 issmall; there is little coupling tending to swing the accelerator gridI5, and it consequently tends to maintain very nearly zero R.-F.potential.

As has already been described and as shown in detail in Fig. 16 theboundary grid i is firmly clamped between the flange 3 and the anodehousing 2, and is therefore physically and definitely at the groundpotential of the housing. The boundary grid and the anode face I3 againform the termini of a resonant line, comprising the housing 2 as itsouter conductor and a cylindrical anode body, designated by the generalreference character I39, within the housing. This resonant line isone-half wavelength long, and may be considered as terminating betweenthe inner face of the flange I and the end I35 of the anode body. Thiswill be recognized as an openended half wave line, and therefore ofextremely high impedance when viewed from either end.

The construction and method of support of the anode body are best shownin Fig. 8. The support is from the midor quarter wavelength point of theanode, i. e., at a potential node, so that there is little tendency forpower to escape from the support structure. Such tendency as there isfor power to leak from the support point is suppressed by either or bothof two methods. First, and preferable in the cases where the tube may bepredesigned to operate at a fixed wavelength, is a movable plate I32mounted on the sliding rod 59 of the Wilson seal first described, andmaking contact with the flange I by means of a spring skirt I33. Thismay be adjusted to bring the node of the resonant line accurately at thepoint of support. This method of preventing direct radiation from theanode was adopted in the first of these devices constructed. It wasquickly found, however, that the plate I32 was more useful as a tuningdevice, and therefore the principle of transmission-line choke supportwas again employed to prevent power escape. In the construction thenadopted and here shown a side tube I40 of relatively large diameter iswelded at substantially the midpoint of the anode housing 2. The sidetube carries a metallic flange I4I, with a glass insulator tube I42fitted against it and in turn carrying a terminal flange I43. Throughthis terminal flange passes a pipe I44 which projects through a passhole I45 in the side of the anode housing and on the end of which theanode body is attached. The action here will be described following themechanical description of the anode, as the expedients adopted arepredicated upon the necessities of the mechanical structure.

From the electrical point of view the anode body is a simple cylinderwith closed ends. Its complexity, as shown in Fig. 8, is due primarilyto the provision for circulating cooling water within it, and to theprovision of what may be termed a rough tuning device.

Owing to the necessity for providing cooling the body itself must bewater-tight, and accordingly it is constructed of a flared cylinder I41,to the flared end of which the anode face I3 is hardsoldered. The otherend of the cylinder is closed by a threaded disc I49.

The supporting pipe I44 enters the flared cylinder I41 through anaperture in the side thereof. The end of the pipe is threaded into aboss I48 on an inner bafiie cylinder I 50, which boss is soldered to theinner wall of the cylinder I47. The boss I48 extends internally to forma cylindrical chamber !5 I which connects by a side pipe I52 through theend I53 of the baffle cylinder, so that water introduced through thepipe I44 is discharged directly against the active face I3 of the anode,and thence is forced around the exterior of the baifle cylinder toreenter its open end. It can then return within the cylinder to enterthe open end of a return pipe I5 3, which is mounted concentricallywithin the pipe I44 by means of a perforated cap I55 which fits over theend of the pipe I44, its lower end passing out through the dischargechamber I5I. The cap compresses a rubber gasket I46, sealing the jointbetween the pipe I44 and the anode body to make it water and vacuumtight.

The upper end of the pipe I54 is centered in the pipe I44 by means of ametal bellows I57 which is sealed to both pipes and. permitsdifferential expansion between the two. Water is introduced into thepipe I44 through a side pipe I59, and its course can be traced by thearrows in the drawings through the outer pipe, the perforations in thecap I55, the side pipe I52, and thence around the balile cylinder I50and back through the central pipe I54.

The action of the mounting follows the principles already set forth,although the application is somewhat different. A disc I00 is connectedto the flange I4! both electrically and mechanically, and carries acylinder ISI. The pipe I44 and the cylinder I 40 and IGI form atransmission line one full wavelength long. Electrically this mightequally well be a half wavelength line, but additional space is neededfor the insulating cylinder I42, which must withstand the full D.-C.anode potential of 20,000 volts or more. The length of this section ismeasured from the anode and its housing, and the impedance at its outerend is very high, so that looking into it from the anode the impedanceis also very high.

This high impedance is connected in shunt across the line formed by theanode body I 30 and anode housing 2 very near the nodal point, where theimpedance of the latter lineis low, and accordingly a very small portionof the current flowing at this point will take the high impedance pathto the outer world.

In other terms, the full wave line is connected so near the node Of themain anode oscillator circuit that only a few volts are eifective acrossits termini, and therefore very small currents will tend to flowtherein, representing a power loss of where V is the small input voltageand Z is the large input impedance. Moreover, since the line is onewavelength long, only the small voltage V will be effective to causeradiation from the radiating system constituted by the end of the line.It should be noted, however, that by deliberately unbalancing the anoderesonator by means of the plate I32 the support systemcan be convertedto a horn antenna which can be

